Conventional technologies will be described below. Conventionally, an evaporated fuel processor is known. The processor guides evaporated fuel from a fuel tank to a canister so that evaporated fuel is adsorbed into an adsorbent which is accommodated in the canister. After that, while a purge control valve is open, the processor introduces (purges) the evaporated fuel adsorbed in the canister into an intake pipe of an internal combustion engine (engine) by use of negative pressure of intake air. Accordingly, the processor prevents release of evaporated fuel into the atmosphere. For an example of an electromagnetic valve, an electromagnetic valve which is incorporated into the evaporated fuel processor is known (see, e.g., JP-A-2006-258135 corresponding to US2006/0207663A1).
As illustrated in FIG. 6, this electromagnetic valve (first example of the conventional technology) includes a valve 103 made of a nonmagnetic material that is engageable with a valve seat 102 of a housing 101; a valve 105 made of a nonmagnetic material that is engageable with a valve seat 104 of this valve 103; a shaft 106 made of a nonmagnetic material extending in an axial direction; and an electromagnetic actuator including a movable core 107 that is made of a magnetic material and coupled with the valve 105 via this shaft 106 to be movable integrally at least with the valve 105, a fixed core (a stator core 108 and a magnetic plate 109) made of a magnetic material that slidably holds this movable core 107, and a coil 110 that generates magnetic force, which attracts the movable core 107 to an attraction part side of the stator core 108, upon supply of electric power.
A spring 111 that urges the valve 103 in a valve opening direction is disposed between the housing 101 and the valve 103. A spring 113 that urges the valve 105 in a valve closing direction is disposed between the movable core 107 and a piece 112. A bellows 114 including a cylindrical portion having a bellows shape that can expand and contract in the axial direction is formed integrally with the valve 105. A retainer 115, which is fitted on an outer periphery of the shaft 106, is accommodated in this bellows 114. An annular outer circumferential edge (flange) formed on the actuator side of the bellows 114 is located between the housing 101 and the magnetic plate 109. Accordingly, the bellows 114 is accommodated in a hollow part (valve chamber) of the housing 101 to surround the shaft 106 and the retainer 115 in their circumferential direction.
The valve 105 is configured to be closed or opened corresponding to expansion or contraction movement of the bellows 114. For example, if a before-after pressure difference of the valve 105 (pressure difference between the inside and outside of the bellows 114) is large at the time of valve opening operation that that the valve 105 is disengaged from the valve seat 104 of the valve 103, the bellows 114 cannot contract smoothly, and the valve 105 is thereby not opened. Accordingly, a pressure cancel mechanism that cancels out the before-after pressure difference of the valve 105 is provided for the electromagnetic valve.
The pressure cancel mechanism is configured such that a pressure cancel passage communicates between an internal space of the bellows 114 and a fluid passage 116 of the housing 101. Accordingly, the bellows 114 smoothly makes expansion or contraction movement in the axial direction by the inflow and outflow of fluid between the inside and outside of the bellows 114 through an opening that opens on the actuator side. Therefore, the valve 105 can be opened or closed in accordance with a displacement of the bellows 114. As illustrated in FIG. 6, the pressure cancel passage of the electromagnetic valve includes an opening 121 of the stator core 108, a clearance 122 between the movable core 107 and the stator core 108, a spring chamber 123, a communication hole 124 of the piece 112, an internal space 125 of the piece 112, a pressure release hole of a resin molding 126, and an internal passage of a hose 127. For the purpose of reduction of the operating noise by making the expansion and contraction movement of the bellows 114 serve to produce a damper effect, the electromagnetic valve reduces its operating noise by producing the damper effect through the reduction of a cross-sectional area of a passage from the internal space of the bellows 114 to the pressure cancel passage.
For another example of the electromagnetic valve, an electromagnetic air control valve (electromagnetic valve) having the pressure cancel mechanism is known (see, e.g., JP-A-H11-01360). As illustrated in FIG. 7, this electromagnetic valve includes a valving element 203 that is engageable with a valve seat 202 of a valve Main body 201; a valving element supporting member 204 that supports this valving element 203; and an electromagnetic actuator having a movable core 205 made of a magnetic material that is coupled with the valving element 203 and the valving element supporting member 204 to be movable integrally therewith, a fixed core (a stator core 206 and a housing 207) made of a magnetic material that slidably supports this movable core 205, and a coil 208 that generates magnetic force, which attracts the movable core 205 to an attraction part side of the stator core 206, upon supply of electric power. A spring 211 that urges the valving element 203, the valving element supporting member 204, and the movable core 205 in a valve opening direction is disposed between the valving element 203 and an adjustment screw 209. A spring 212 that urges the valving element 203, the valving element supporting member 204, and the movable core 205 in a valve closing direction is disposed between the movable core 205 and the stator core 206.
An annular diaphragm 215 that separates a hollow part of the valve main body 201 between a pressure cancel chamber 213 and an air passage 214 is disposed in the electromagnetic valve. This diaphragm 215 has an annular central part in its center, and includes an annular outer peripheral part on its outer side. In this electromagnetic valve, the central part of the diaphragm 215 is held between the valving element 203 and the movable core 205, and the outer peripheral part of the diaphragm 215 is clamped at a contact part between the valving element 203 and the housing 207. Accordingly, the pressure cancel chamber 213 is formed, so that the diaphragm 215 can be easily attached in the hollow part of the valve main body 201. In the pressure cancel mechanism of the electromagnetic valve, the pressure cancel chamber 213 and the air passage 214 communicate through a pressure hole 221 of the valving element supporting member 204 and a pressure hole 222 of the movable core 205. The pressure hole 221 is configured as a longitudinal hole passing through the valving element supporting member 204 in its axial direction. The pressure hole 222 includes a vertical hole with a bottom part that extends in the axial direction of the movable core 205, and a horizontal hole that extends in a direction perpendicular to the axial direction of the movable core 205 to face the pressure cancel chamber 213.
The electromagnetic valve described in JP-A-2006-258135 (first example of the conventional technology) is a configuration which delays responsivity of the movable core 107. Thus, the electromagnetic valve is not suitable for the case of improvement of control responsivity. The fluid in the internal space of the bellows 114 needs to flow into the pressure cancel passage (including the spring chamber 123, the communication hole 124, the internal space 125, the pressure release hole, and the internal passage of the hose 127) through the narrow clearance 122 between the movable core 107 and the stator core 108. Moreover, the pressure cancel passage is configured to pass through the hose 127 disposed outside the electromagnetic valve, and the valve is therefore disadvantageous in its size and cost.
In the electromagnetic valve described in JP-A-H11-013604 (second example of the conventional technology), the horizontal hole needs to be formed through the movable core 205. Since the horizontal hole is formed in a radial direction of the core 205 perpendicular to the axial hole (central hole) of the movable core 205, change of a direction of the core 205 and re-chuck of the core 205 are necessary at the time of boring through the movable core 205, and high manufacturing costs of the electromagnetic valve are thereby required. If a gap (clearance) between the movable core 205 and the fixed core (the stator core 206 and the housing 207) is made smaller than FIG. 7 to improve efficiency of a magnetic circuit although the pressure cancel passage is not formed on a rear side of the movable core 205, the fluid (e.g., air and oil) on the rear side needs to flow into the pressure cancel chamber 213 through the small clearance at the time of the valve operation. Accordingly, the damper effect is produced, and thus, an elapsed time (valve opening response time) after the start of energization of the coil 208 until the valving element 203 actually begins to open is increased.
For the purpose of solving the above-described issue, the central passage of the movable core 205 may be configured to be a through hole passing through the movable core 205 in its axial direction to communicate between the space of the movable core 205 on the valving element side (lower end side in FIG. 7) and the space of the movable core 205 on the rear side. However, for its coexistence with the pressure cancel passage, similar to the above, cost rising due to boring of the horizontal hole is unavoidable.